Methods of Swine Slurry Application: Uniformity and Efficiency.

Ammonia volatilization causes a decrease of crop available N from surface applied swine slurry. We studied the effects of two application methods, splash-plate and incorporation, on N application uniformity and efficiency, and crop N use efficiency. Swine slurry was distributed using the two application methods at rates of 30 t/ha and 60 t/ha in a Typic Xerofluvent soil in an irrigated semiarid Mediterranean environment. Ammonium concentrations were analyzed in soil samples taken from the upper 0.3 m soil layer at points located 0.2 m apart in three transect lines per plot (9 m long for splash-plate method and 5 m long for incorporation method), perpendicular to the slurry application direction, four days after slurry application (4DASA). Changes in soil mineral N content were studied in soil cores taken from the upper 0.3 m soil layer at twelve different times during the growing season. Wheat grain yield, above ground biomass and total N uptake were used to evaluate N crop use efficiency. The uniformity of application, calculated from the soil ammonium concentrations 4DASA, following the methodology of Merriam and Keller (1978), was 71% for the incorporation method and 37% for the splash-plate method. The efficiency of N application, estimated as the fraction of ammonium recovered in the soil samples relative to the amount applied with the slurry, was 90% for the incorporation method and 45% for the splash-plate method. The slurry rate had a significant effect on crop yield and N uptake. However, the method of slurry application did not affect the crop yield and N uptake, neither the soil mineral N content. The higher application efficiency of the incorporation method did not return higher wheat N use efficiency. A larger N immobilization when incorporating the slurry with the soil could explain these results.